The present invention relates to dielectric resonant devices having cavities which contain dielectric cores, filters and duplexers using the dielectric resonant devices, and communication apparatuses using the filters and the duplexers.
Hitherto, dielectric resonant devices have been used as filters and the like used in microwave bands, each dielectric resonant device having a ceramic cavity which has an open face, contains a dielectric core, and is provided with a conductive film, the cavity being covered by a metallic panel at the open face thereof.
In particular, a dielectric resonant device is disclosed in, for example, Japanese Unexamined Patent Application Publication Nos. 9-51201 and 8-222905, in which a metallic panel provided with a coupling loop and the like formed thereon and having a coefficient of linear expansion substantially the same as that of a material for resonator is directly connected by soldering to an electrode formed on an open face of a ceramic cavity. Another dielectric resonant device is disclosed in, for example, Japanese Unexamined Patent Application Publication Nos. 8-181513 and 8-65017, in which an open face of a ceramic cavity is covered by a printed circuit board provided with a coupling loop and the like formed thereon, and a conductive film of the ceramic cavity and the printed circuit board are connected to each other by soldering via a grounding plate therebetween, or the grounding plate is screwed to the substrate side.
However, a problem has been found in the above dielectric resonant device disclosed in Japanese Unexamined Patent Application Publication Nos. 9-51201 and 8-222905, in that since the thermal capacity of the ceramic cavity is large when the dielectric resonant device is large, a large temperature gradient is likely to be generated when soldering and a stress is applied to the joint part, whereby cracks causing breakages are easily produced in the joint part during use for a long time. The dielectric resonant device disclosed in Japanese Unexamined Patent Application Publication Nos. 8-181513 and 8-65017 requires a plurality of the grounding plates, thereby increasing the number of components and increasing manufacturing costs as a whole.
There is a problem in either dielectric resonant device of above, in that the manufacturing efficiency significantly decreases when the shape of the open face of the ceramic cavity is complex. The tendency toward the decrease of the efficiency is remarkable particularly when a regulated lead-free solder is used.
According to the present invention, a dielectric resonant device comprises a ceramic cavity having an open face and coated with a conductive film, the cavity containing a dielectric core; a conductive panel for covering the open face; and a resilient grounding plate sandwiched between the open face of the cavity coated with the conductive film and the conductive panel. The conductive panel is fixed to the cavity in such a manner as to be pressed thereto. The open face of the cavity and the conductive panel with the grounding plate therebetween which is connected to the conductive film formed on the open face of the cavity are brought into resilient contact with each other, whereby the problem of an unreliable contact part caused by soldering and the problem of an increased number of components and increased manufacturing costs due to the increased number of grounding plates are overcome, and manufacturing operations can be easily performed even when the shape of the open face of the cavity is complex.
According to the present invention, the grounding plate may be provided with projections which project in such a manner as to increase the thickness of the grounding plate in a direction of a gap between the conductive film provided on the open face and the conductive panel. With this arrangement, the overall grounding plate is provided with high resiliency by the projections in addition to the resiliency-which the material of the grounding plate has in itself, whereby superior electrical connection (grounding) can be maintained between the conductive film provided on the open face of the cavity and the conductive panel.
According to the present invention, the open face may comprise opposing first and second open faces of the cavity which are parallel to each other, and the conductive panel may comprise first and second panels for covering the first and second open faces, respectively, the first and second panels being fixed by screws. With this arrangement, a dielectric resonant device including the opposing two conductive panels, each provided with a coupling loop and the like, is obtainable. The cavity is not necessarily provided with a particular structure for mounting panels, and the panels can be mounted simply by fixing the panels to the cavity so as to sandwich the cavity.
The screws may be provided in a plurality of positions, at least some of the screws being disposed in the positions at which the screws pass through the inside of the cavity. With this arrangement, the overall size of the dielectric resonant device is prevented from increasing due to additional spaces for the screws.
The dielectric core in the cavity may be formed integrally therewith with two dielectric columns disposed perpendicular to each other so as to form a cross; the cross-section of sidewalls of the cavity, parallel to the open face of the cavity, is substantially uniform; the two dielectric columns are each provided with concavities formed in the sidewalls of the cavity and extending along the axis of the dielectric column; some of the screws are disposed inside the concavities and outside the cavity; and the other screws which are not inside the concavities are disposed inside the cavity. With this arrangement, the overall dielectric resonant device is prevented from being enlarged due to additional spaces for the screws passing outside the cavity.
According to the present invention, filter and duplexer individually comprise the dielectric resonant devices according to the present invention.
A communication apparatus comprises the filter or duplexer according to the present invention.